The present invenion relates to turbomachines and, more particularly, to improved means for retaining rotor blades in rotor slots.
It is well known in the art that turbomachinery rotor assemblies are comprised of a plurality of circumferentially adjacent blades having tangs disposed in individual slots around the periphery of a rotor disc. Each blade is held in place by a retaining mechanism which serves to prevent axial migration and egress of the blade tang from the rotor slot while the rotor assembly is subject to the high centrifugal forces associated with rotation under engine operating conditions.
Many different and varied retaining mechanisms have been utilized in the past to retain the rotor blades securely affixed to the rotor disc. Some of these prior art mechanisms incorporated metal strips with bent ends and suffered from the disadvantage of being non-reuseable; that is to say, when the rotor assembly was disassembled, new locking mechanisms had to be installed as replacements for those which were repeatedly bent and flexed in prior installation and removal operations. These retaining mechanisms proved to be unreliable and their replacement at each disassembly was expensive. Other prior art retaining mechanisms were comprised of a multiplicity of components and hence assembly thereof into the rotor assembly was difficult and time-consuming
Still other retaining mechanisms known in the prior art utilized elongated members with enlarged bearing lugs disposed at each end. The elongated member was disposed within the rotor disc slot between the blade tang and the bottom of the slot. The entire member, once in the slot, was rotated or translated into an installed position where the bearing lugs overlapped a portion of the rotor disc. Retaining mechanisms of this type exhibit load limits dependent upon the available space between the blade tang and the bottom of the disc slot. More specifically, the maximum loads which can safely be imposed upon the retaining mechanism are dependent upon the cross-sectional area of the elongated member. The maximum cross-sectional area of the member is limited by the available space between the blade tang and the bottom of the disc slot. Since the aforementioned available space is usually small, use of retaining mechanisms of this type are not readily applicable in instances where high loading of the retaining mechanism is anticipated.
Other retaining mechanisms in the prior art have been arranged to transfer some of the loads, associated with aerodynamic and centrifugal forces, to portions of the blade itself. Blade retainers of this type have not proven to be fully satisfactory since the blades utilized in such arrangements must be designed to accommodate the additional loads and as a result are bulky and heavy.